The present invention relates generally to electric motors and in particular to the drive circuitry for providing drive current to DC (direct current) motors.
A conventional brushless DC motor typically includes a stator comprising a set of windings (“stator windings”) and a rotor comprising a set of permanent magnets. A position detector provides an indication of the rotational position of the rotor; e.g., a Hall effect device is typically used, though other position detection techniques such as optical detection can be used.
It is conventionally known that when the stator windings are properly energized by driving currents of electricity through them, the resulting attractive and repulsive forces between the poles of the rotor and the energized coils will cause the rotor to rotate. By properly synchronizing changes in the direction of the driving currents through the stator windings, sustained rotation of the rotor can be achieved. The timing of the changes to the driving current is based on the rotor position.
The energizing of the stator windings is referred to as “commutation,” and occurs in periodic fashion whereby the direction of the driving currents through the stator windings periodically reverse. Thus, for a brushless DC motor, a first commutation period involves driving current through the stator windings in a first direction, and then during a second commutation period the current that is driven through the stator windings is reversed. The circuitry used to provide the drive currents to the motor is typically referred to as the “drive circuit.” Commonly owned U.S. Pat. No. 6,611,117 disclosed a novel method and apparatus whereby the drive circuit included a microcontroller used to produce the drive current, and is entirely incorporated herein by reference for all purposes.